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Australia leads Flight 370 search01:15

• The airline could have hired another company to perform the necessary maintenance;

• It could have done nothing.

If it chose thethird, and the original batteries were still driving the pingers when the Boeing 777-200ER disappeared from radar screens, their life probably would have dropped from 30 days to 25 or 20 days, Patel said.

The pingers would not die immediately but would continue to emit signals with "progressively lower output levels until the unit shuts down," he said.

Malaysia Airlines did not respond to a question from CNN about the devices. But the airline said in an e-mail last week, "We are unaware of any issue with the ULB (underwater locator beacon) or its batteries."

"This battery is not replaceable," the airline said. "The battery is built-in inside the (pinger) and installed by OEM -- Original Equipment Manufacturer."

On Saturday, the Malaysia Airlines CEO said the acoustic pinger batteries on the airlines' black boxes were due for replacement in June 2014.

"We can confirm there is a maintenance program. Batteries are replaced prior to expiration," Ahmad Jauhari Yahya said.

What happens if they sputter out? Is there any hope left of finding the jet that was carrying 239 people when it disappeared from view on March 8?

What are pingers, and how do you find them?

All commercial airplanes are required to carry pingers -- underwater locator beacons -- to help investigators find them should they crash into water. One is attached to the flight data recorder, another to the cockpit voice recorder.

The pings sound about once per second and can be detected from 2 nautical miles away by towed pinger locators, or TPLs.

The pinger locator is equipped with a sensor that looks like a 35-inch, 70-pound yellow stingray. It can recognize the flight recorder's chirps up to 20,000 feet below the water surface.

An Australian ship is dragging a TPL in the Indian Ocean that is on loan from the United States.

Photos:The search for MH370

Photos:The search for MH370

Two years after Malaysia Airlines Flight 370 went missing, a relative of one of the passengers burns incense in Beijing on March 8, 2016. Flight 370 vanished on March 8, 2014, as it flew from Kuala Lumpur, Malaysia, to Beijing. There were 239 people on board.

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Photos:The search for MH370

On July 29, police carry a piece of debris on Reunion Island, a French territory in the Indian Ocean. A week later, authorities confirmed that the debris was from the missing flight.

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Photos:The search for MH370

Staff members with the Australian Transport Safety Bureau examine a piece of aircraft debris at their laboratory in Canberra, Australia, on July 20. The flap was found in June by residents on Pemba Island off the coast of Tanzania, and officials had said it was highly likely to have come from Flight 370. Experts at the Australian Transport Safety Bureau, which is heading up the search for the plane, confirmed that the part was indeed from the missing aircraft.

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Photos:The search for MH370

In late February, American tourist Blaine Gibson found a piece of plane debris off Mozambique, a discovery that renewed hope of solving the mystery of the missing flight. The piece measured 35 inches by 22 inches. A U.S. official said it was likely the wreckage came from a Boeing 777, which MH370 was.

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Relatives of the flight's passengers console each other outside the Malaysia Airlines office in Subang, Malaysia, on February 12, 2015. Protesters had demanded that the airline withdraw the statement that all 239 people aboard the plane were dead.

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Photos:The search for MH370

A police officer watches a couple cry outside the airline's office building in Beijing after officials refused to meet with them on June 11, 2014. The couple's son was on the plane.

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Members of the media scramble to speak with Azharuddin Abdul Rahman, director general of Malaysia's Civil Aviation Department, at a hotel in Kuala Lumpur, Malaysia, on May 27, 2014. Data from communications between satellites and the missing flight was released the day before, more than two months after relatives of passengers said they requested it be made public.

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Operators aboard the Australian ship Ocean Shield move Bluefin-21, the U.S. Navy's autonomous underwater vehicle, into position to search for the jet on April 14, 2014.

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A member of the Royal New Zealand Air Force looks out of a window while searching for debris off the coast of western Australia on April 13, 2014.

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The HMS Echo, a vessel with the British Roya; Navy, moves through the waters of the southern Indian Ocean on April 12, 2014.

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A Royal Australian Air Force AP-3C Orion, on a mission to drop sonar buoys to assist in the search, flies past the Australian vessel Ocean Shield on April 9, 2014.

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A relative of a missing passenger cries at a vigil in Beijing on April 8, 2014.

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Australian Defense Force divers scan the water for debris in the southern Indian Ocean on April 7, 2014.

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A towed pinger locator is readied to be deployed off the deck of the Australian vessel Ocean Shield on April 7, 2014.

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A member of the Royal New Zealand Air Force looks at a flare in the Indian Ocean during search operations on April 4, 2014.

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On March 30, 2014, a woman in Kuala Lumpur prepares for an event in honor of those aboard Flight 370.

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The sole representative for the families of Flight 370 passengers leaves a conference at a Beijing hotel on March 28, 2014, after other relatives left en masse to protest the Malaysian government's response to their questions.

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A member of the Royal Australian Air Force is silhouetted against the southern Indian Ocean during the search for the missing jet on March 27, 2014.

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Flight Lt. Jayson Nichols looks at a map aboard a Royal Australian Air Force aircraft during a search on March 27, 2014.

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People in Kuala Lumpur light candles during a ceremony held for the missing flight's passengers on March 27, 2014.

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Malaysian Prime Minister Najib Razak, center, delivers a statement about the flight on March 24, 2014. Razak's announcement came after the airline sent a text message to relatives saying it "deeply regrets that we have to assume beyond any reasonable doubt that MH 370 has been lost and that none of those onboard survived."

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Grieving relatives of missing passengers leave a hotel in Beijing on March 24, 2014.

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A passenger views a weather map in the departures terminal of Kuala Lumpur International Airport on March 22, 2014.

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A Chinese satellite captured this image, released on March 22, 2014, of a floating object in the Indian Ocean, according to China's State Administration of Science. It was a possible lead in the search for the missing plane. Surveillance planes were looking for two objects spotted by satellite imagery in remote, treacherous waters more than 1,400 miles from the west coast of Australia.

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Satellite imagery provided by the Australian Maritime Safety Authority on March 20, 2014, showed debris in the southern Indian Ocean that could have been from Flight 370. The announcement by Australian officials raised hopes of a breakthrough in the frustrating search.

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Another satellite shot provided by the Australian Maritime Safety Authority shows possible debris from the flight.

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A distraught relative of a missing passenger breaks down while talking to reporters at Kuala Lumpur International Airport on March 19, 2014.

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On March 18, 2014, a relative of a missing passenger tells reporters in Beijing about a hunger strike to protest authorities' handling of information about the missing jet.

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U.S. Navy crew members assist in search-and-rescue operations in the Indian Ocean on March 16, 2014.

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Members of the Chinese navy continue search operations on March 13, 2014. After starting in the sea between Malaysia and Vietnam, the plane's last confirmed location, search efforts expanded west into the Indian Ocean.

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A Vietnamese military official looks out an aircraft window during search operations March 13, 2014.

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Malaysian air force members look for debris near Kuala Lumpur on March 13, 2014.

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Relatives of missing passengers wait for the latest news at a hotel in Beijing on March 12, 2014.

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A member of the Vietnamese air force checks a map while searching for the missing plane on March 11, 2014.

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A Vietnamese air force plane found traces of oil that authorities had suspected to be from the missing Malaysia Airlines plane, the Vietnamese government online newspaper reported on March 8, 2014. However, a sample from the slick showed it was bunker oil, typically used to power large cargo ships, Malaysia's state news agency, Bernama, reported on March 10, 2014.

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A U.S. Navy Seahawk helicopter lands aboard the USS Pinckney to change crews on March 9, 2014, before returning to search for the missing plane in the Gulf of Thailand.

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Buddhist monks at Kuala Lumpur International Airport offer a special prayer for the missing passengers on March 9, 2014.

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Members of a Chinese emergency response team board a rescue vessel at the port of Sanya in China's Hainan province on March 9, 2014.

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The rescue vessel sets out from Sanya in the South China Sea on March 9, 2014.

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Malaysian Prime Minister Najib Razak, center, arrives to meet family members of missing passengers at the reception center at Kuala Lumpur International Airport on March 8, 2014.

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A relative of two missing passengers reacts at their home in Kuala Lumpur on March 8, 2014.

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Not only will the batteries powering the pinger die after about 30 to 45 days, but their sound can be obscured by weather, noise or silt.

And pinger locators must be towed slowly -- it could take days to cover the 150-mile (240-kilometer) track that officials have identified as the latest, best guess for where the plane might be.

"It is a very slow proceeding search, 2 to 3 knots depending on the depth that you want the hydrophone, that tow pinger locator trailed at," said Capt. Mark M. Matthews, the U.S. Navy's head of TPL operations. "It's going to take time. ... Again, we're searching on what information we do have, our best guess at where it would have been lost. It's the best we can do at this time."

So is all hope lost in finding a plane after the pinger dies?

No. Take, for example, Air France Flight 447, which disappeared in 2009 as it was flying from Rio de Janeiro to Paris.A towed pinger locator looked -- without success.

But two years later, searchers using an autonomous underwater vehicle found the flight data recorder and the bulk of the wreckage hundreds of miles off Brazil.

What other high-tech gadgets can searchers use to find Malaysia Airlines Flight 370?

An Australian search ship has an autonomous underwater vehicle called the Bluefin-21, which can scour the ocean bed looking for signs of wreckage.

But the AUV, on loan from the United States, would be deployed only if the searchers get a clear fix on the beacons sending out the pings, Matthews said.

AUVs are typically used in the oil and gas industry to conduct deep-water oilfield surveys.

"The smaller ones are only going to go down to about 5,000 feet," analyst David Soucie said. "The next class is a much more expensive, much larger device. It's 15 by 25 feet because it adds a lot of battery capability and a lot of hydraulic capability."

One of the most sophisticated AUVs owned by Phoenix International was activated and flown to Perth, Australia, to help with the search for Flight 370. The device is yellow, 17.2 feet long and has an in-air weight of 1,600 pounds.

It can search 20,000 feet below the water surface and travel 2 to 4.5 knots, using side-scan sonar to map the seafloor. Its probe, equipped with a still camera, moves rapidly.

"A picture will scroll, and you will see the seafloor be painted in front of you," said Jami Cheramie, vice president of systems development and IT support for C&C Technologies Inc., whose AUV has been used to search for plane debris in the past.

Have these underwater vehicles found plane wrecks in the past?

Yes. AUVs helped find the downed Air France flight, the wreckage of the plane that was carrying Italian fashion designer Vittorio Missoni when it disappeared last year off Venezuela, and the HMS Ark Royal, a ship sunk by a German U-81 submarine in World War II. The AUV provided black-and-white images of the wreckage site.

Will the mystery of Flight 370 be solved once the data recorders are found?

Not necessarily. The voice recorders retain only the last two hours of recordings. And, since officials believe Flight 370 flew almost seven hours beyond the point where something went terribly wrong, crucial data have almost certainly been erased.

On the positive side, the depletion of the battery will not wipe out data. Data has been known to survive years in harsh sea water conditions on modern recorders.